Absolute Temperature Scale

A temperature scale that uses the absolute zero of temperature as the lowest temperature.

Absolute Zero

Theoretically the lowest attainable temperature.

Acceptor Impurities

Impurities that can accept electrons from semiconductors.

Accuracy

The closeness of a measurement to the true value of the quantity that is measured.

Acid

A substance that yields hydrogen ions (H⁺) when dissolved in water.

Acid Ionization Constant

The equilibrium constant for the acid ionization.

Acid-Base Reaction

A reaction between an acid and a base.

Actinide Series

Elements that have incompletely filled 5f subshells or readily give rise to cations that have incompletely filled 5f subshells.

Activated Complex

The species temporarily formed by the reactant molecules as a result of the collision before they form the product.

Activation Energy

The minimum amount of energy required to initiate a chemical reaction.

Activity Series

A summary of the results of many possible displacement reactions.

Actual Yield

The amount of product actually obtained in a reaction.

Addition Polymers

A reaction in which one molecule adds to another.

Adhesion

Attraction between unlike molecules.

Alcohol

An organic compound containing the hydroxyl group —OH.

Aldehydes

Compounds with a carbonyl functional group and the general formula RCHO, where R is an H atom, an alkyl, or an aromatic group.

Aliphatic Hydrocarbons

Hydrocarbons that do not contain the benzene group or the benzene ring.

Alkali Metals

The Group 1A elements (Li, Na, K, Rb, Cs, and Fr).

Alkaline Earth Metals

The Group 2A elements (Be, Mg, Ca, Sr, Ba, and Ra).

Alkanes

Hydrocarbons having the general formula C_nH_2n+2, where
n = 1,2, . . . .

Alkenes

Hydrocarbons that contain one or more carbon-carbon double bonds. They have the general formula C_nH_2n, where n = 2,3, . . . .

Alkynes

Hydrocarbons that contain one or more carbon-carbon triple bonds. They have the general formula C_nH_2n-2, where n = 2,3, . . . .

Allotropes

Two or more forms of the same element that differ significantly in chemical and physical properties.

Alloy

A solid solution composed of two or more metals, or of a metal or metals with one or more nonmetals.

Alpha Particles

See alpha rays.

Alpha Rays

(a) - Helium ions with a positive charge of 12.

Amalgam

An alloy of mercury with another metal or metals.

Amides

A group of organic compounds.

Amines

Organic bases that have the functional group ONR₂, where R may be H, an alkyl group, or an aromatic group.

Amino Acids

A compound that contains at least one amino group and at least one carboxyl group.

Amorphous Solid

A solid that lacks a regular three-dimensional arrangement of atoms or molecules.

Amphoteric

The ability of a species to act as an acid or a base.

Amphoteric Oxide

An oxide that exhibits both acidic and basic properties.

Amplitude

The vertical distance from the middle of a wave to the peak or trough.

Angular Momentum Quantum Number

The shape of the orbital.

Anion

An ion with a net negative charge.

Anode

The electrode at which oxidation occurs.

Antibonding Molecular Orbital

A molecular orbital that is of higher energy and lower stability than the atomic orbitals from which it was formed.

Aqueous Solution

A solution in which the solvent is water.

Aromatic Hydrocarbon

A hydrocarbon that contains one or more benzene rings.

Arrhenius Acid

A substance that ionizes in water to produce H⁺ ions

Arrhenius Base

A substance that ionizes in water to produce OH^- ions

Atmospheric Pressure

The pressure exerted by Earth’s atmosphere.

Atom

The basic unit of an element that can enter into chemical combination.

Atomic Mass

The mass of an atom in atomic mass units.

Atomic Mass Unit

A mass exactly equal to 1/12th the mass of one carbon-12 atom.

Atomic Number

(Z) - The number of protons in the nucleus of an atom.

Atomic Orbital

The wave function (C) of an electron in an atom.

Atomic Radius

One-half the distance between the two nuclei in two adjacent atoms of the same element in a metal. For elements that exist as diatomic units, the atomic radius is one-half the distance between the nuclei of the two atoms in a particular molecule.

Aufbau Principle

As protons are added one by one to the nucleus to build up the elements, electrons similarly are added to the atomic orbitals.

Avagadro’s Number

6.022 X 10²³; the number of particles in a mole.

Avogadro’s Law

At constant pressure and temperature, the volume of a gas is directly proportional to the number of moles of the gas present.